In the 1920s Otto Warburg first proposed non-oxidative metabolism of glucose as a unique feature of tumors (Warburg, (1930) Ueber den stoffwechsel der tumoren (London: Constable); Warburg, (1956) Science 123, 309-314). This hypothesis has since caused significant interest and although mechanistic links are still, almost 100 years later, under investigation, a high glucose flux of tumor is today exploited clinically, using PET imaging of 18F-2-deoxyglucose uptake as a diagnostic tool for solid tumors.
Lately abnormal energy processing of cancer cells has been given new attention (Vander Heiden, et al. (2009) Science 324, 1029). The hypoxic microenvironment and consequential lactate accumulation resulting from altered tumor metabolism are predictive for both metastatic potential and therapy resistance, and thus survival of cancer patients (Brown, (1999) Cancer Res. 59, 5863-5870; Walenta & Mueller-Klieser, (2004) Semin. Radiat. Oncol. 14, 267-274; Walenta et al., (2004) Curr. Med. Chem. 11, 2195-2204). Targeting of these hypoxic and acidotic tumor areas, has therefore drawn attention as a complement to anti-proliferative treatments (see e.g. Pan & Mak, (2007) Sci. STKE 381, pe14; Bache et al., (2008) Curr. Med. Chem. 15, 322-338 for reviews).
Known inhibitors of glycolysis are 2-deoxyglucose and 2-bromo-pyruvate targeting hexokinase (Liu et al., (2001) Biochemistry 40, 5542-5547; Liu et al. (2002) Biochem. Pharmacol. 64, 1745-1751; Xu et al., (2005) Cancer Res. 65, 613-621; Ramanathan et al., (2005) Proc. Natl. Acad. Sci. USA 102, 5992-5997). Fructose-2,6-bisphosphate (F-2,6-P2) plays a regulatory role in glucose metabolism by relieving ATP inhibition of phosphofructokinase-1. The levels of F-2,6-P2 are regulated by the bifunctional enzyme family 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFKFB1-4).
Of these four isozymes, mainly PFKFB3 and PFKFB4 are of particular interest for playing a role in cancer. Anti-sense treatment against PFKFB3 was shown to reduce tumor growth rate in vivo (Chesney et al., (1999) Proc. Natl. Acad. Sci. USA 96, 3047-3052) Also, a decreased anchorage independent growth was shown for siRNA treated fibroblasts (Telang et al., (2006) Oncogene 25, 7225-7234). It has recently been demonstrated that the proinflammatory cytokine interleukin (IL)-6 enhances glycolysis in mouse embryonic fibroblasts and human cell lines (Ando et al. J Nippon Med Sch (2010), 77, (2), 97-105) indicating the potential for PFKFB3 inhibitors as anti-inflammatory agents. Hypoxia is a prominent feature in rheumatoid arthritis (RA) synovium, and induce significant changes in the expression of PFKFB3 and PFKFB 4 (Del Rey et al., (2010) Arthritis & Rheumatism 62, 3584-3594).
Minchenko et al. showed increased expression of PFKFB4 mRNA in breast and colon malignant tumors as compared to corresponding non-malignant tissue counterparts as well as in several cancer cell lines. PFKFB4 was reported to be strongly responsive to hypoxia (Minchenko et al., (2004) FEBS Lett. 576, 14-20); Minchenko et al., (2005), Biochemie 87, 1005-1010; Bobarykina et al., (2006), Acta Biochemica Polonica 3, 789-799). Recently, Telang et al. showed decreased levels of F-2,6-P2 and lactate as well as decreased tumor growth following siRNA silencing of PFKFB4 (Telang, S. et al, (2010) US2010/0267815 A1).
Only a small number of specific inhibitors of the kinase activities of PFKFB3 and PFKFB4 have been identified. In one study, an alkylating inhibitor, N-bromoacetylethanolamine phosphate, was used as a tool to investigate the binding sites of the kinase and phosphatase domains of PFKFB3 and was demonstrated to irreversibly inactivate PFK-2 (Sakakibara et al. (1984), J. Biol. Chem 259, 14023-14028). The compound is a competitive inhibitor of PFK-2 with respect to F6P but a noncompetitive inhibitor with respect to ATP. Analogues of this compound, N-(2-methoxyethyl)-bromoacetamide, N-(2-ethoxyethyl)-bromoacetamide and N-(3-methoxypropyl)-bromoacetamide, have demonstrated in vivo activity with increased survival rate of P388 transplant BDF1 mice (Hirata et al. (2000) Biosci. Biotechnol. Biochem. 64, 2047-2052).
A crystal structure of the PFKFB3*ADP*phosphoenolpyruvate complex was described by Kim et al. (Kim et al. (2007), J. Mol. Biol. 370, 14-26). This paper also described the crystal structures of PFKFB3*AMPPCP*fructose-6 phosphate complex where β,γ-methylene-adenosine 5′-triphosphate (AMPPCP) constituted a non-hydrolysable ATP-analogue.
A drug-like compound was described (Clem et al. (2008) Mol. Cancer Ther. 7, 110-120; Chesney et al. (2008) WO 2008/156783) where 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one (3PO), by computational methods, was identified as a PFKFB3 inhibitor. Administration of 3PO reduced the intracellular concentration of F-2,6-P2, glucose uptake, and growth of established tumors in vivo. Recently, substituted benzindoles were described as inhibitors of PFKFB3. The benzindoles were shown to inhibit proliferation in several cancer cell lines, inhibit glucose uptake as well as to reduce tumor growth in vivo in tumor models (Chand et al. (2011) WO2011/103557A1).